1. FIELD OF THE INVENTION
The present invention relates generally to an apparatus for collecting and treating vaporized fuel in a fuel tank without releasing the fuel vapor into the atmosphere. More particularly, the present invention pertains to a testing apparatus for testing a fuel vapor treating device.
2. DESCRIPTION OF THE RELATED ART
A fuel vapor treating device, typically mounted on a vehicle, collects and treats vaporized fuel in a fuel tank without releasing the fuel vapor into the atmosphere. As shown in FIG. 14, a typical apparatus has a canister 73 that draws in and collects fuel vaporized in a fuel tank 71 through a vapor line 72. The canister 73 is filled with an adsorbent 74 comprised of activated carbon or the like. A purge line 75, extending from the canister 73, is connected to an intake passage 77 of an engine 76. The canister 73 first adsorbs the vaporized fuel drawn in through the vapor line 72. The canister 73 collects fuel and discharges only the residual gas, from which fuel components (particularly hydrocarbon, HC) have pen extracted, into the atmosphere through a hole 78. The fuel collected in the canister 73 is purged into the intake passage 77 by way of the purge line 75 during operation of the engine 76. A purge control valve 79, provided in the purge line 75, adjust the flow rate of the fuel conveyed through the purge line 75 in accordance with the requirements of the engine 76.
In this typical treating device, damage or disconnection of the vapor line 72 may lead to a degradation in the airtightness, or sealing, of the treating device. This may result in insufficient treatment of the vaporized fuel.
Japanese Unexamined Patent Publication 6-108930 describes an apparatus that tests for malfunctions such as those described above. As shown in FIG. 15, a testing apparatus used for fuel vapor treating devices includes a fuel tank 81, a canister 82, a vapor line 83, and ex purge line 84. The purge line 84 connects the canister 8Z to an intake passage 80. A purge vacuum switching valve (VSV), or purge control valve 85, is selectively opened by an electronic control unit (ECU) 86 when the engine 76 is running. A vapor control valve 87, which is a check valve and is provided in the vapor line 83, controls the flow of vaporized fuel directed toward the canister 82 from the fuel tank 81. A difference in pressure between the fuel tank 81 side and the canister 82 side of the vapor control valve 87 opens the valve 87 and causes the vaporized fuel to flow therethrough. Opening of the valve 87 allows fuel vapor to flow into the canister 82 from the tank 81. Another control valve 90 is provided in a passageway that bypasses the vapor control valve 67 and is controlled by the ECU 86. When the control valve 90 is opened with the vapor control valve 87 in a closed state, the valve 90 allows fuel vapor to flow into the canister 82 from the tank 01. The testing apparatus includes a pressure sensor 88, which separately detects the interior pressure in the tank side of the vapor control valve 87 and the canister side of the vapor control valve 87. That is, a three-way valve 89, connected to the pressure sensor 88, including a port connected to the vapor line 83 at the side of the tank 81 and another port connected to the vapor line 83 at the side of the canister 82. The pressure sensor 88 selectively detects the tank pressure and canister pressure when the ECU 86 switches the side which the three-way valve 89 is connected to in accordance with its requirements. The ECU 86 separately tests the sealed state of the tank side and the sealed state of the canister side based on the detected value of the tank pressure and the canister pressure.
The principle for performing testing of the sealing in the tank side will now be described. When fuel vaporizes in the tank 81 with the control valve 90 in a closed state, the tank side pressure exceeds a predetermined reference value. Holes such as punctures in the vapor line 83 would inhibit the tank side pressure from exceeding the predetermined reference value. Therefore, it is possible to test the tank side sealing by having the ECU 86 judge whether the tank side pressure, detected by the pressure sensor 88, exceeds the reference value.
When the vehicle is moving, the running state of the vehicle or the condition of the road surface causes the fuel in the tank to surge back and forth, or sway. The swaying and splashing of the fuel in the tank 81 changes the interior pressure in the tank side (the tank side pressure). Frequent swaying of feel fluctuate the tank side pressure as illustrated by a continuous line L1 in FIG. 16(a). Although occasional pressure fluctuations are negligible, frequent fluctuations as illustrated by line L1 in FIG. 16(a) result in inaccurate testing of the sealing in the tank side.
Recently, a testing apparatus that discontinues testing of the sealing in the tank side when there is frequent fuel swaying in the tank has been proposed. The apparatus is provided with a counter for indicating how often the fuel in the tank surges and the amplitude of the surges. The counter has a counter value that is incremented in accordance with the absolute value of change in the tank pressure. When the counter value reaches a predetermined value, the occurrence of fuel surges is judged to be so frequent that the sealing of the tank side cannot be accurately tested. In this case, the ongoing testing is discontinued.
When fuel in a tank surges frequently and causes the tank pressure to fluctuate, for example, as illustrated by the continuous line L1 in FIG. 16(a), the counter value increases as illustrated by a continuous line C1 in FIG. 16(b) in accordance with the pressure fluctuations. If the counter value exceeds a predetermined value CT, the surges are judged to be too frequent.
If there is a malfunction related with the sealing of the fuel tank or the vapor line, the tank pressure will be substantially equal to the atmospheric pressure. In this case, frequent surges cause only insignificant pressure fluctuations such As the ones illustrated by a dashed line L2 in FIG. 16(a). However, the counter value increases in accordance with the pressure fluctuations (surges of the fuel in the tank) as illustrated by a dashed line C2.
In addition to fuel surges in the tank as described above, the fuel is violently swayed by rapid acceleration, rapid deceleration and bumpy road conditions. If there is no malfunction related with the sealing, the violent swaying of the fuel temporarily and quickly raises the tank pressure. Such a change in the tank pressure is illustrated by a broken line L3 in FIG. 16(a). When the fuel tank is exposed to wind or rain, the temperature of the fuel drops. This quickly lowers the tank pressure.
With no malfunction related with the sealing, abrupt pressure changes in the fuel tank as described above cause the counter value to unpredictably and rapidly increase as illustrated by a broken line C3. When the counter value exceeds the predetermined value CT, the testing of the sealing in the tank side is discontinued. In other words, the testing is stopped before detecting that there is no malfunction related with the sealing of the tank side. Therefore, the normality of the sealing in the tank side is not detected.